The present embodiments relate to a continuously digitally adjustable phase actuator for radio-frequency applications.
Magnetic resonance tomographs are imaging devices that, for imaging an examination object, align nuclear spins of the examination object with a strong external magnetic field and through a magnetic alternating field excite the nuclear spins into precession around this alignment. The precession or return of the spins from this excited state into a state with lower energy creates a magnetic alternating field as a response, which is received via antennas.
With the aid of magnetic gradient fields, a spatial encoding is impressed on the signals, which subsequently makes an assignment of the received signal to a volume element possible. The received signal is then evaluated, and a three-dimensional imaging representation of the examination object is provided. Local antennas (e.g., local coils) may be used for receiving the signal. The local antennas are arranged directly on the examination object for achieving a better signal-to-noise ratio.
The spins are excited by a magnetic alternating field created by a power amplifier and irradiated into the examination region by an antenna. In this process, powers of several Kilowatts are usual. The power is partly created via a number of separate power amplifiers. Signals of the separate power amplifiers are to have a precisely defined phase relationship. The individual antennas are also controlled in an antenna matrix, for example, with precisely defined phase displacements relative to one another, in order to achieve a predefined spatial field distribution of the excitation field.
In such cases, an individual control signal may be created digitally separately for each individual antenna output, but this requires a considerable outlay in circuit technology and signal processing resources, however.
Obtaining different control signals from a single input signal by phase displacement may also be provided. This is achieved by a control of variable phase actuators, usually by connectable discrete phase shifters with a fixed value. As the increment of the phase displacement to be achieved decreases, however, the number of discrete phase shifters increases, and thus, the circuit outlay increases significantly.